Peripheral nerve mucoid degeneration/intra-neural pseudocyst/intra-neural ganglion/intra-neural ganglion cyst: solving the enigma

Lesions of peripheral nerve with cysts filled with mucoid material has been termed as peripheral nerve mucoid degeneration/intra-neural ganglion cyst. There is lack of awareness of the condition, and the pathogenesis still remains elusive to clinicians and radiologists, leading to high rates of misdiagnosis and mistreatment. Although no clinical symptoms or signs are diagnostic, it must be included into the differential diagnosis of lesions arising adjacent to nerves and presenting with compressive neuropathy. Characteristic signs and intra-articular connection can be located on radiological investigations, clinching the diagnosis. Wrong diagnosis and mistreatment of this condition can lead to a more aggressive approach with devastating consequences. Two cases affecting the common peroneal nerve presenting with insidious onset of foot drop were operated. Presentation, diagnosis, and management of these cases are discussed along with the current understanding of the lesion. Both the cases were diagnosed as intra-neural ganglion cyst of common peroneal nerve. MRI was done in these cases, and intra-articular connection was established in one case. The lesion was decompressed along with excision of intra-articular connection in one of the cases. Post-operatively patients had a good recovery with improvement in sensations and power of dorsiflexors. MRI is the investigation of choice for diagnosis of intra-neural ganglion cyst. Connection to the adjacent joint can be visualized in majority of cases. Various methods have been reported for management but cyst incision and ligation or excision of intra-articular branch is currently the best modality of treatment in these cases. Level of evidence: Level V: therapeutic; diagnostic; risk/prognostic study.